1. Field of the Invention
The present invention relates to an active matrix light emitting device. More specifically, the invention relates to a structure of the part from which luminescence is extracted.
2. Description of the Related Art
A light emitting device using luminescence out of an electroluminescent element (a light emitting element) attracts attention as a display device of wide viewing angle and low power consumption.
There are an active matrix type and a passive matrix type as driving methods for a light emitting device which is mainly used for display. In a light emitting device of an active matrix type driving method, emission state, non-emission state or the like can be controlled in every light emitting element. Therefore, it can be driven with smaller power consumption than a passive matrix light emitting device, and it is suitable for being mounted not only as a display portion of a small electric appliance such as a mobile phone but also as a display portion of a large-size television receiver or the like.
In addition, in an active matrix light emitting device, each light emitting element is provided with a circuit for controlling the drive of the respective light emitting element. The circuit and the light emitting element are disposed over a substrate so that extraction of luminescence to the outside is not prevented by the circuit. Light-transmitting insulating layers are laminated in a part superposing with the light emitting element, and luminescence is emitted outside through the insulating layer. These insulating layers are provided in order to form a transistor which is a component of the circuit, a circuit element such as a capacitor element or a wiring.
Luminescence sometimes interferes each other multiple times according to the difference in a refractive index of each insulating layer. As a result, a problem that an emission spectrum varies depending on a viewing angle with respect to a side from which luminescence is extracted and visibility of an image displayed in the light emitting device is deteriorated is caused.
In addition, deterioration in visibility of an image due to the difference of a refractive index of each layer occurs also in a passive matrix display device. For example, Reference 1: Japanese Patent Laid-Open No. Hei 7-211458 raises a problem that external light and luminescence are reflected at an interface due to the difference of a refractive index of each layer which constitutes a light emitting element, and visibility is deteriorated. Patent Document 1 also suggests a light emitting element with an element structure capable of solving the above problem.